Toxic cyanobacteria blooms in drinking water supplies have been an increasing public health concern all over the world. Human populations can be exposed to microcystins, an important family of cyanotoxins, mainly by oral ingestion. However, inhalation from recreational water and hemodialysis can represent other routes. This study investigated changes in respiratory mechanics, histology, protein phosphatase (PP) 1 and 2A activity and microcystin in lung of adult mice injected intraperitoneally (i.p.) with microcystin-LR. Thirty-six mice were divided into control (CTRL) and test (CYANO) groups. CTRL group received an i.p. injection of saline and the CYANO group received 40 microg MCYST-LR/kg i.p. After 2 and 8 h, and 1, 2 and 4 days after toxin injection, six mice from each group were sampled for analyses. Resistive and viscoelastic pressures, static and dynamic elastances augmented at 2 h in CYANO and so remained until day 4. Alveolar collapse and inflammatory cell infiltration were found 2h after the injection, reaching peak values at 8 h. However, no microcystin or inhibition of PPases could be detected in mice lungs. In conclusion, MCYST-LR led to a rapid increase in lung impedance and an inflammatory response with interstitial edema and inflammatory cell recruitment in mice.